In U.S. Pat. No. 4,826,129, there is disclosed a structure of faucet for automatic water supply and stoppage, in which a controller actuates a two-way electromagnetic valve to lift a mandrel, permitting the water to flow out when the user's hands are close to the front of said faucet, and the valve is capable of automatic locking and can be actuated by only an instantaneous trigger of electric energy so as to achieve the practical purpose of saving power, safety and convenience. However, the instantaneous pressure change and the suction effect resulting from speed flowing of water flow tend to pull the mandrel to displace downward, causing the outlet passage to be not fully opened. As a consequence, desired maximum water flow rate can not be achieved. If to increase the capacity of the electromagnetic valve, power consumption will be relatively increased.